This invention relates generally to design, construction, manufacturing cost and performance improvements for multi-circuit cylindrical signal and power electrical connector components used in both sliding and rolling interface transfer mechanisms. More particularly, the invention relates to improved current transfer devices for conducting currents between stator and rotor members of mechanisms where the interface between the two is by means of conventional rolling couplers or by sliding brushes.
Slip rings have a long history of applications for the transfer of electrical energy between two mutually rotating members. This transfer is affected by conducting the electrical signals and power from one member to the other through a sliding interface. One or both of these members is cylindrical with the circuit components configured into the cylinder, or cylinders. More recently rolling elements have been introduced at each circuit interface for the same function with rolling instead of sliding conductive components. Recent examples of rolling interface configurations are disclosed in several U.S. Patents. These describe rolling electrical interface configurations for both low level signals and for power transfer. Even the advantages provided by these roll ring transfer units cannot always be realized for some applications because of manufacturing costs and lead times related to the construction process.
The large variety of electrical transfer requirements, specified by the broad field of users introduces another problem for both sliding and rolling transfer, which has both design and cost ramifications. Each new design of the transfer mechanism requires new tooling, fixtures, and molds. This results in long delivery schedules from definition to unit delivery as well as increased manufacturing costs. Since envelope parameters of diameter, length and shape as well as performance requirements of voltage, current, waveform, frequency and electrical resistance noise (or signal quality) establish the design requirements of the transfer unit, each application configuration and design is unique. This situation identifies why new non-recurring design and tooling costs accrue with each new set of specifications.
An existing means of fabricating slip ring sets is to position or mold the rings in place. As the number of circuits increases, and if the rings require machining and plating prior to molding, the total manufacturing costs increase. In an attempt to reduce this cost, the rings are sometimes machined as a molded assembly. This often results in a problem related to loosening of the rings from the molding bond during fabrication with attendant scrap costs. Lead wires connected to the conductive rings are sometimes integrated into the molded assembly. If a wire breaks or looses connection with the ring, or shorts to other wires during the manufacturing process, the entire component must usually be scrapped with obvious cost implications. These considerations result in increased manufacturing costs and force long order-to-delivery time.
One prior art patented configuration consists of stacked sets of rings and spacers to form an axial series of single non-shielded circuits. This design provides annulus channels for rolling interconnection balls between the inner and the outer circuit rings. Although this configuration provides for repeated use of common contact rings and spacers and the elimination of a molding process, which can effect cost reductions, the leads must be attached, and the rings machined and plated, individually. This drives the cost up because of the fact that the majority of plating cost is associated with the labor required to handle individual components. Additionally, the cost of the configuration is adversely affected by the labor required to feed the lead wires through the individual rings and spacers during the assembly process. This configuration does not lend itself to electrical shielding. The assembly complexity and associated high manufacturing cost of the described configuration is easily visualized for transfer units which require  greater than 100 circuits.
Another problem associated with the molded assembly technique is the method of attaching the lead wires to the individual circuit rings by molding the wires into the ring support matrix and casting the wire ends into the rings as they are formed by plating. This process does not allow corrections to be made if the lead connection is faulty, or, as is sometimes the case, when the component connection becomes intermittent when the unit is exposed to a cyclic temperature environment.
High voltage insulative resistance requirements are difficult to meet in adjacent circuits when the axial pitch is small. This latter requirement is forced by specifications, which require a large number of circuits in a small axial space. A radially extending barrier between adjacent circuits is required to provide adequate high voltage insulation qualities. This is necessary to increase the path length, which a given contaminant must bridge between adjacent circuits before electrical shorting can occur. Additionally the greater wear debris of slip rings exacerbates the electrical insulative break down problem of adjacent circuits when adequate barriers are not provided. When a rotary transfer mechanism is used in severe environmental conditions, even wiper seals built into the housings are not able to prevent a measure of moisture and contaminants from entering the unit. This often results in electrical bridging between adjacent circuits and electrical insulative failure of the unit if adequate barriers are not provided. Circuit barriers are difficult to mold or machine into the module without breakage because of the small axial thickness which is available in the design. In addition, the barrier must be formed from the same insulating plastic material the rings are set in which results in a brittle, and easily damaged, protective wall. This condition can exist for both slip rings and roll rings.
The inner ring assembly of present rotary electrical transfer mechanisms is characteristically manufactured as a single assembly. Since many transfer unit designs require  greater than 100 circuits the probability is high that one or more circuits will be damaged during the manufacturing process. Example sources of this damage are irreversible machining errors, internal shorting in the molded wiring, miswires in the ring connections, broken internal lead/ring connections and ring damage caused by inadvertent contact with a tool or measuring device. Even though the damage may involve only one of many circuits, it will result in scrapping of the entire ring assembly if it cannot be repaired properly and the unit salvaged. The level of expense, both schedule and fiscal, is great enough as to sometimes warrant a reassignment of lead ring connections in the related system to establish a work-around. This is obviously not a desirable solution.
When a high frequency transfer requirement has been defined it is important that proper shielding of the leads to the ring be established. This requires the continuation of the shield on a given lead to a position as close as possible to the ring the lead is attached to. It is usually not possible to use shielded or sleeved wire within a molded assembly since the structural integrity of the lead-to-mold is reduced. This situation reduces the effectiveness of the shielding of the circuits within the assembly. It is also important that the number of connections of each lead from contact ring to the external connector be minimized. When the contact ring is molded into place along with the leads it is often necessary to use solid wire within the molded region of the assembly and to terminate the lead at the perimeter of the molding. This not only necessitates an undesirable additional connection point but a potential failure mechanism since mechanical stress imposed by forces imposed by the external leads, or cables, can fatigue the terminal embedded in the molding.
It is an object of the present invention to provide improvements of manufacturing cost of both slip ring and roll ring cylindrical electrical transfer sub assemblies associated with tooling and parts cost. This improvement is accomplished by the use of geometrically simple torodial shaped conducting rings, insulators and circuit connection members.
It is an additional object of this invention to provide improvements of subassembly geometry such that the subassembly radial runout errors are less than those of the components from which the subassembly has been made. This situation allows lower cost components to be used for a given set of assembly geometry requirements.
It is another object of the present invention to provide decreased design time of new electrical transfer mechanisms by the use of common components, which may be arranged in a variety of configurations to achieve the desired circuit configurations.
It is yet an additional object of the present invention to decrease manufacturing lead-time of transfer units. This objective can be realized by the modularization of the current transfer components and the use of circuit contact rings and insulating spacers, which have a wide variety of applications.
It is yet another object of the present invention to provide extended operational lifetime of electrical transfer mechanisms associated with reduced sensitivity to wear product and general debris contaminants. This objective is achieved by the construction technique, which allows the use of structurally sound barriers between circuits.
It is yet another object of the present invention to provide reduced environmental sensitivity associated with a greater resistance to circuit to circuit electrical shorting resulting from water, salt spray, oil films or other environmental borne debris by the use of high barriers between circuits.
It is an additional object of the present invention to provide multi-functions of the geometrically simple components such as connecting tabs, which also provide lead wire channels and geometry control.